Enhanced chloride selective membrane

ABSTRACT

There is provided a chloride selective membrane including an epoxide-based matrix reacted with a stoichiometric amount of an amino compound and an activator such that the epoxide-based matrix comprises a number of quaternary ammonium groups.

CROSS REFERENCE TO RELATED APPLICATIONS

The subject application is a continuation of U.S. Serial No. 17/652,937,filed Mar. 1, 2022; which is a continuation of U.S. Serial No.15/572,000, filed Nov. 6, 2017, now U.S. Pat. No. 11,293,892, issuedApr. 5, 2022; which is a U.S. National Stage Application under 35 USC §371 of International Application No. PCT/US2016/032814, filed May 17,2016; which claims benefit under 35 USC § 119(e) of U.S. ProvisionalApplication No. 62/162,843, filed May 18, 2015. The entire contents ofthe above-referenced patent applications are hereby expresslyincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to the field of diagnostic testing,and more particularly to improved chloride selective membranes,electrodes incorporating the same, and processes for making the same.

BACKGROUND

Ion selective electrodes (ISEs) typically comprise a plasticized polymermatrix comprising an ionophore or other ionic species selective for theion of interest. Ion selective electrodes have been developed, forexample, for the detection and/or determination of sodium (Na⁺),potassium (K⁺), magnesium (Mg²⁺), calcium (Ca²⁺), and chloride (Cl⁻).

In a number of diagnostic assays for such ionic species, interferentsthat may provide a positive or negative bias for the analyte of interestare of particular concern. As such, one requirement is that the relevantion selective electrodes provide sufficient selectivity for a particularion. In addition, it is now understood that certain types of samples mayadversely affect ion selective electrodes. For example, chloride ionselective electrodes have been shown to be prone to the extraction ofplasticizers and ionophores out of the membrane by certain compounds,thereby causing the sensitivity of the membrane to be compromised.Further, particularly with biological fluids such as serum, urine,plasma, and whole blood, it is believed that lipophilic anionic speciessuch as bicarbonate, salicylate, and heparin may further interfere withchloride detection by binding to active sites on the membrane of theelectrode.

U.S. Pat. No. 7,384,523 proposed one solution for a chloride sensorhaving a chloride selective membrane, the chloride selective membranecomprising an epoxy resin and an amine agent selected from polyamides,amidoamines, and mixtures thereof. In order to provide sufficientquaternary amine functional groups for the detection of chloride, theamine agent is provided in stoichiometric excess. Further solutions forproviding chloride sensors with improved sensitivity, stability,reproducibility, and use life are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of thedrawings that show:

FIG. 1 shows an exemplary sensor comprising a chloride selectivemembrane in accordance with an aspect of the present invention.

FIG. 2 shows the two-week stability of a sensor calibrated every 4 hoursin simulated serum samples. in accordance with an aspect of the presentinvention.

FIG. 3 shows < 10% interference from 60 mg/dL salicylate spiked serumsamples for a sensor over a period of 15 days in accordance with anotheraspect of the present invention.

FIG. 4 illustrates the stability of a chloride sensor upon exposure toheparinized plasma samples in accordance with another aspect of thepresent invention.

DETAILED DESCRIPTION

In one aspect, the present inventors have developed chloride selectivemembranes comprising an epoxide-based matrix reacted with astoichiometric amount of an amino compound and an activator such thatthe epoxide-based matrix comprises a number of quaternary ammoniumgroups. The reaction between the quaternary ammonium sites and chloridein a sample generates a potentiometric signal, which is utilized todetermine an amount of chloride in the sample. The membranes asdescribed herein exhibit excellent sensitivity, stability,reproducibility, and improved use life for the ion selective electrode,particularly with biological samples. In one aspect, the membranes asdescribed herein may form a structural barrier that substantially limitsdiffusion of potential lipophilic interferents such as bicarbonate,salicylate, heparin, and proteins into the membranes so as to improvethe use life and performance of the membranes.

In accordance with another aspect, there is provided a chlorideselective membrane comprising stoichiometric amounts of an epoxy resin,an amino compound, and an activator, wherein the activator promotesreactions between the components to provide the membrane with aplurality of quaternary functional groups.

In accordance with another aspect, there is provided a process forforming a chloride sensitive membrane comprising combiningstoichiometric amounts of an epoxy resin, an amino compound, and anactivator, wherein the activator promotes reactions between thecomponents to provide the membrane with a plurality of quaternaryfunctional groups.

As used herein, the term “about” refers to a value that is ± 10% of thestated value.

As used herein, the term “alkyl” refers to a saturated aliphatichydrocarbon chain and a substituted saturated aliphatic hydrocarbonchain that can be either straight-chain or branched-chain.

As used herein, the term “aryl” refers to a group containing a singlearomatic ring or multiple aromatic rings that are fused together,directly linked, or indirectly linked.

As used herein, by the phrase “effective amount,” it is meant an amountof material suitable for bringing about an intended result.

As used herein, the term “stoichiometric amount” refers to an amount ofa component theoretically needed to react with all of the reactivegroup(s) of at least a second component.

The epoxide-based matrix of the membrane may comprise any composition(e.g., compound, polymer, or the like) comprising one or more epoxidegroups which may be reacted with an amino compound, an activator, and/ora product of a reaction between the amino compound and the activator asare described herein. In an embodiment, the epoxide-based matrixcomprises an epoxy resin having a predetermined number of epoxide groupsper molecule. For example, in an embodiment, the epoxy resin may havemore than one epoxide group per molecule and in another embodiment, morethan about 1.5 epoxide groups per molecule. Also, the epoxy resin may besaturated or unsaturated, linear or branched, aliphatic, cycloaliphatic,aromatic or heterocyclic, and substituted or unsubstituted. Exemplaryepoxy resins for use herein include but are not limited to2,2-bis(4-hydroxyphenyl) propane (bisphenol-A);2,2-bis(4-hydroxy-3-tert-butylphenyl) propane; 1,1-bis(4-hydroxyphenyl)ethane; 1,1-bis(4-hydroxyphenyl) isobutane; and1,1-bis(4-hydroxy-3-alkylphenyl) ethane. Numerous epoxy resins arecommercially available and may be used in the membranes described hereinsuch as EPON™ epoxy resins available from Resolution PerformanceProducts; DER™ epoxy resins available from Dow Chemical Company; andAraldite™ epoxy resins available from Huntsman Advanced Materials. In aparticular embodiment, the epoxy resin may comprise DER™ 331, whichcomprises liquid reaction product between epichlorohydrin and bisphenolA (DER 331). The present inventors have found that DER™ 331 provides aparticularly stable epoxide-based matrix for the membranes describedherein.

The amino compound may comprise any suitable compound comprising one ormore amino groups which will react with the epoxide groups of theepoxide-based matrix. The amino compounds may comprise a primary amine,second amine, and/or a tertiary amine. While primary and/or secondaryamines may be provided in the membranes since primary and/or secondamines may ultimately be converted to the desired quaternary ammoniumsites in successive reactions, in an embodiment, the amino compoundcomprises a tertiary amine which may be directly converted to thedesired quaternary ammonium sites. Starting with tertiary amines allowsfor a single step to provide the desired quaternary ammonium sites andsimplifies the reactions necessary to produce the desired membranes.

In an aspect, the tertiary amine comprises a polyamine, wherein anunsaturated and unsubstituted carbon chain is present between twoadjacent amino groups in the polyamine. While not wishing to be bound bytheory, it is believed that the larger the carbon chain, the more rigidthe resulting chemical network. A rigid chemical network may aid informing a structural barrier to prevent interferents such asbicarbonate, salicylate, and heparin from penetrating the membrane.

In certain embodiments, the amino compound may comprise a diamine. Inthis way, the amino compound may again comprise multiple amino groups,which during reaction with the epoxide groups of the epoxide-basedmatrix, may provide the desired quaternary ammonium sites. Thequaternary ammonium sites are selective for chloride in a sample. In anembodiment, the quaternary ammonium sites may be of the formula:

NR₄ ⁺, wherein R = hydrogen, an alkyl group, or an aryl group, forexample.

In a particular embodiment, the amino compound may comprise a tertiarypolyamine such as a tertiary diamine. Exemplary tertiary polyamines foruse herein include but are not limited toN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA),N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA), andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA).

The activator may comprise any suitable compound which accelerates theproduction of quaternary functional groups in the epoxide-based matrixrelative to a process without the activator. In an embodiment, theactivator comprises a compound which reacts with the amino compound toproduce two ionic species, each of which will react with theepoxide-group containing monomers or compounds provided by theepoxide-based matrix. In an embodiment, the activator comprises amercaptan compound. In a particular embodiment, the activator comprisesa polymercaptan compound such as a polymercaptan having four thiolgroups. Exemplary polymercaptans include but are not limited topentaerythritol tetrakis (3-mercaptopropionate), trimethylolpropanetris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate). While not wishing to be bound by theory, itis also believed the activator may contribute to maintaining the desiredstructure in the epoxide-based matrix. The tridimensional structure ofthe epoxide-based matrix may be a contributing factor in how effectivethe matrix is as a barrier to potential interferents such asbicarbonate, salicylate, and heparin. A more limited porosity, forexample, will aid in acting as a barrier to the interferents.

In certain embodiments, the amino compound may be protonated by theactivator to provide a pair of reactive species, each of which may reactwith epoxide group-containing compounds to ultimately produce thedesired epoxide-based matrix having quaternary functional groups. In aparticular exemplary embodiment, the preparation of the membrane takesplace according to the following reactions.

First, an effective amount of the amino compound and the activator reactto provide a pair of reactive ionic species:

This may be referred to as the “activation stage.” Following this, thereactive species may react with epoxide monomers of the epoxide-basedmatrix according to the following reactions (“polymerization stage”):

In the above reactions, in one embodiment, R₁ may be an alkyl group; R₂may comprise an alkyl group; and R₃ may comprise a diglycidal ether.

In accordance with an aspect of the present invention, the aminocompound, the activator, and epoxide-based resin are provided instoichiometric amounts relative to one another. As noted above, knownepoxy-based chloride selective membranes believed it necessary to employa stoichiometric excess of components to provide the desired quaternaryammonium functional groups for the membrane. Aspects of the presentinvention provide a membrane with sufficient quaternary ammonium groupsvia use of stoichiometric amounts of the reactants only, therebyrealizing material and production time and cost savings.

In one aspect, the amino compound and the activator are provided in astoichiometric amount relative to the number of epoxide groups in theepoxide-based matrix. In an embodiment, this stoichiometric amount is ina range of from 0.5:1 to about 1.5: 1, such as about 1:1.

In another aspect, the amino compound and the activator may be providedin stoichiometric amounts relative to one another. In an embodiment, thestoichiometric ratio of the amino compound relative to an amount of theactivator may also be from about 0.5:1 to about 1.5: 1, such as about1:1.

In certain embodiments, the membrane may further include an effectiveamount of a solvent for the components of the membrane in order to bringthe membrane to a suitable viscosity for placement on an associatedsubstrate for production of an electrode. In an embodiment, the solventcomprises an organic solvent utilized for known ion selective membranes,such as benzaldehyde, cyclohexanone, isophorone, xylene,tetrahydrofuran, toluene, or the like.

The various embodiments of the chloride selective membranes as describedherein may be incorporated into any suitable structure for an ionselective electrode and/or sensor as are well known in the art to form achloride sensitive electrode. Typically, the described chlorideselective membrane is produced by dispensing the membrane (or componentsthereof separately to form the membrane) on an inert substrate as isknown in the art to form a portion of the electrode. In certainembodiments, the membrane may be applied as a layer in an electrodealong with a polymer layer, an electrode layer, a conductor layer,and/or a transducer layer on a substrate. Exemplary structures intowhich the membranes described herein may be incorporated are further setforth in U.S. Pat. Nos. 7,384,523; 6,767,450; and 5,102,527; U.S.Published Pat. Application No. 20140158536; and WO2014092543 A1, forexample. The entirety of each of these references is hereby incorporatedby reference.

FIG. 1 shows an exemplary sensor 10 comprising a chloride selectivemembrane as described herein. The sensor 10 comprises a housing 12,which may be formed from any suitable inert material. Disposed withinthe housing 12 are fluid connectors 14 and electrical connectors 19 asare known in the art. The fluid connectors 14 allow for introduction ofa sample and/or other fluids into the sensor 10 and travel of the sampleand/or other fluids to a fluid channel member 16. A sensor plate 20comprising a chloride selective membrane 18 as described herein isarranged such that a sample introduced to the sensor 10 travels to thefluid channel member 16 and over the sensor plate 20. In an embodiment,the sensor plate 20 comprises a ceramic substrate or other substrateformed from an inert material. The electrical connectors 19 areconfigured to detect a potentiometric signal generated upon reactionbetween the quaternary ammonium sites on the membrane 18 and chloride inthe sample. The signal may be delivered to a data collection system asis known in the art for processing.

In accordance with another aspect, the electrode comprising a chlorideselective membrane as described herein may be disposed in a cartridgeemploying a plurality of additional electrodes for the detection of atleast one ionic species selected from the group consisting of sodium,potassium, magnesium, and calcium, or the like, for example. In stillother embodiments, the electrode comprising a chloride selectivemembrane as described herein may be disposed in a cartridge employing aplurality of additional electrodes for the detection of one or morespecies or properties such as one or more of pH, potassium ion, sodiumion, magnesium ion, and the like, for example.

Electrodes comprising the chloride selective membranes as describedherein are suitable for use with any samples suspected of having anamount of chloride therein. In an embodiment, the electrodes aresuitable for use with biological samples. The biological sample may befrom a human or non-human subject. Moreover, the sample may be derivedfrom whole blood, serum, plasma, sputum, lymphatic fluid, semen, vaginalmucus, feces, urine, spinal fluid, saliva, stool, cerebral spinal fluid,tears, mucus, and the like; biological tissue such as hair, skin,sections or excised tissues from organs or other body parts; and soforth. It is appreciated that the sample may undergo any pre-treatmentor preparation necessary to submit the sample to the electrode would beappreciated by one skilled in the art.

In another aspect, there is provided processes for forming a chloridesensitive membrane having the components described above. In anembodiment, the process comprises combining stoichiometric amounts of anepoxy resin, an amino compound, and an activator, wherein the activatorpromotes reactions between the components to provide the membrane with aplurality of quaternary functional groups. In certain embodiments, theamino compound and activator may be combined and allowed to react priorto their combination with the epoxy resin.

Aspects of the present invention are demonstrated by the followingexamples, which are not intended to be limiting in any manner.

EXAMPLES Example 1: Preparation of a Chloride Sensor Membrane andElectrode Preparation of a Chloride Ion Selective Membrane Sensor

Modified bispenol A epoxide resin (DER 331) (Dow Chemical (Midland,MI)), N,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA), pentaerythritoltetrakis (3-mercaptopropionate), were purchased from Sigma Aldrich (St.Louis, MO). Stoichiometric amount of epoxy resin and curing agent(tertiary amine and mercaptan) was calculated from the averageequivalent epoxide or amine hydrogen weight (EEW or AHEW) of eachcomponent. Into a 20 mL glass vial, 1.9 g DER 331, 0.61 gpentaerythritol tetrakis (3-mercaptopropionate), 0.43 gN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA) were added. A 0.5 mL ofsolvent THF was added and stirred to create a homogenous mixture. Themixture was manually or automatically coated onto the surface of anAg/AgCl electrode on a disposable ceramic substrate. The substrate washeated at 80 C for 5 minutes to facilitate the cross-linking reaction.

Example 2: Epoxy-Based Chloride Sensor Selectivity

The above-mentioned substrate with epoxy membrane was mounted into aplastic cartridge with a rubber fluid channel membrane. The finishedproduct was tested on a Siemens Dimension Vista Clinical ChemistryAnalyzer. It was auto-calibrated every 4 hours during a 14 daysstability study. The selectivity of such chloride sensor was measuredagainst a spiked horse serum sample of high levels of salicylate (60mg/dL).

FIG. 2 shows the two-week stability of a sensor formed according toExample 1 calibrated every 4 hours in simulated serum samples (x axis =days).

FIG. 3 shows < 10% interference of a sensor upon exposure to a 60 mg/dLsalicylate spiked serum samples over a period of 15 days.

Example 3: Epoxy-Based Chloride Sensor Selectivity

Heparin in plasma sample could degrade conventional ISE sensors bypenetrating into the selective PVC membrane and therefore results in asensitivity degradation and/or false recovery. In this example, a highvolume of 5000 plasma sample was measured using the proposed epoxychloride sensor. During a 14-day study, 500 plasma samples were measuredevery day. The sensor maintained a stable slope and recovered withminimal bias.

FIG. 4 illustrates the stability of the sensor formed according toExample 1 upon exposure to heparinized plasma samples in accordance withan aspect of the present invention (x axis = days).

While various embodiments of the present invention have been shown anddescribed herein, it will be obvious that such embodiments are providedby way of example only. Numerous variations, changes and substitutionsmay be made without departing from the invention herein. Accordingly, itis intended that the invention be limited only by the spirit and scopeof the appended claims.

The invention is a chloride selective electrode comprising a chlorideselective membrane. The chloride selective membrane comprises anepoxide-based matrix reacted with a stoichiometric amount of an aminocompound and an activator such that the epoxide-based matrix comprises anumber of quaternary ammonium groups.

The amino compounds of the membrane may comprise a tertiary amine. Thetertiary amine may be a member selected from the group consisting ofN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA),N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA), andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA). Further, the tertiaryamine may comprise a polyamine, wherein an unsaturated and unsubstitutedcarbon chain is present between two amino groups in the polyamine.

The activator of the membrane may comprise a mercaptan compound. Themercaptan compound may comprise a member selected from the groupconsisting of pentaerythritol tetrakis (3-mercaptopropionate),trimethylolpropane tris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate).

The epoxide-based matrix of the membrane may comprise an epoxy resin.Further, the epoxy resin may comprise a liquid reaction product betweenepichlorohydrin and bisphenol A (DER 331).

The amino compound to the activator in the membrane may comprise astoichiometric ratio from about 0.5:1 to about 1.5: 1, including a ratioof 1:1.

The amino compound and the activator relative to the number of epoxidegroups in the epoxide-based matrix in the membrane may comprise astoichiometric ratio from about 0.5:1 to about 1.5: 1, including a ratioof 1:1.

The above chloride selective electrodes may be part of a sensor assemblywhich also comprises at least one additional sensor for detecting anionic species selected from the group consisting of sodium, potassium,magnesium, and calcium.

In another embodiment, the invention is a chloride selective electrodecomprising a chloride selective membrane, the membrane comprisingstoichiometric amounts of an epoxide-based matrix, an amine, and anactivator, wherein the activator promotes reactions between thecomponents to provide the membrane with a plurality of quaternaryfunctional groups.

The amino compounds of the membrane may comprise a tertiary amine. Thetertiary amine may be a member selected from the group consisting ofN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA),N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA), andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA). Further, the tertiaryamine may comprise a polyamine, wherein an unsaturated and unsubstitutedcarbon chain is present between two amino groups in the polyamine.

The activator of the membrane may comprise a mercaptan compound. Themercaptan compound may comprise a member selected from the groupconsisting of pentaerythritol tetrakis (3-mercaptopropionate),trimethylolpropane tris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate).

The epoxide-based matrix of the membrane may comprise an epoxy resin.Further, the epoxy resin may comprise a liquid reaction product betweenepichlorohydrin and bisphenol A (DER 331).

The amino compound to the activator in the membrane may comprise astoichiometric ratio from about 0.5:1 to about 1.5: 1, including a ratioof 1:1.

The amino compound and the activator relative to the number of epoxidegroups in the epoxide-based matrix in the membrane may comprise astoichiometric ratio from about 0.5:1 to about 1.5: 1, including a ratioof 1:1.

The above chloride selective electrodes may be part of a sensor assemblywhich also comprises at least one additional sensor for detecting anionic species selected from the group consisting of sodium, potassium,magnesium, and calcium.

A further embodiment is a process for forming a chloride sensitivemembrane comprising:

combining stoichiometric amounts of an epoxide-based matrix, an aminocompound, and an activator, wherein the activator promotes reactionsbetween the components to provide the membrane with a plurality ofquaternary functional groups.

The combining step may comprise combining the amino compound and theactivator to allow the amino compound and the activator to react; andadding the reacted amino compound and activator to the epoxide-basedmatrix to form the plurality of quaternary functional groups.

In the process, the amino compounds may comprise a tertiary amine. Thetertiary amine may be a member selected from the group consisting ofN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA),N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA), andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA). Further, the tertiaryamine may comprise a polyamine, wherein an unsaturated and unsubstitutedcarbon chain is present between two amino groups in the polyamine.

In the process, the activator may comprise a mercaptan compound. Themercaptan compound may comprise a member selected from the groupconsisting of pentaerythritol tetrakis (3-mercaptopropionate),trimethylolpropane tris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate).

In the process, the epoxide-based matrix may comprise an epoxy resin.Further, the epoxy resin may comprise a liquid reaction product betweenepichlorohydrin and bisphenol A (DER 331).

In the process, the amino compound to the activator in the membrane maycomprise a stoichiometric ratio from about 0.5:1 to about 1.5: 1,including a ratio of 1:1. Further, the amino compound and the activatorrelative to the number of epoxide groups in the epoxide-based matrix inthe membrane may comprise a stoichiometric ratio from about 0.5:1 toabout 1.5: 1, including a ratio of 1:1.

What is claimed is:
 1. A chloride selective membrane for a chlorideselective electrode that detects chloride in multiple biologicalsamples, wherein the chloride selective membrane is provided with aplurality of quaternary functional groups, and wherein the chlorideselective membrane comprises: an epoxide-based matrix comprising anepoxy resin having a predetermined number of epoxide groups permolecule; a mixture of an amino compound and an activator dispensed ontoa surface of the epoxide-based matrix, wherein the amino compound andactivator are present in the mixture in a stoichiometric amount relativeto the number of epoxide groups in the epoxide-based matrix, and whereinthe stoichiometric amount is in a range of from about 0.5:1 to about1.5:1, and wherein the mixture comprises reactive species; and whereinthe chloride selective membrane is stable for at least 14 days uponexposure to at least one biological sample.
 2. The chloride selectivemembrane of claim 1, wherein the amino compound comprises a tertiaryamine.
 3. The chloride selective membrane of claim 2, wherein thetertiary amine comprises a member selected from the group consisting ofN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA);N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA); andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA).
 4. The chlorideselective membrane of claim 2, wherein the tertiary amine comprises apolyamine, and wherein an unsaturated and unsubstituted carbon chain ispresent between two amino groups in the polyamine.
 5. The chlorideselective membrane of claim 1, wherein the activator comprises amercaptan compound.
 6. The chloride selective membrane of claim 5,wherein the mercaptan compound comprises a member selected from thegroup consisting of pentaerythritol tetrakis (3-mercaptopropionate),trimethylolpropane tris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate).
 7. The chloride selective membrane of claim1, wherein the epoxy resin comprises a liquid reaction product betweenepichlorohydrin and bisphenol A (DER 331).
 8. The chloride selectivemembrane of claim 1, wherein the inert substrate is a ceramic substrate.9. A process for forming a chloride selective membrane of a chlorideselective electrode that detects chloride in at least one biologicalsample, the process comprising the steps of: forming a layer of anepoxide-based matrix, wherein the epoxide-based matrix comprises anepoxy resin having a predetermined number of epoxide groups permolecule; separately combining an amino compound and an activator toform a mixture and allowing the amino compound and the activator toreact and produce reactive species prior to contact with theepoxide-based matrix, wherein the amino compound and activator arecombined in a stoichiometric amount relative to the number of epoxidegroups in the epoxide-based matrix, and wherein the stoichiometricamount is in a range of from about 0.5:1 to about 1.5:1; and dispensingthe mixture containing the reactive species onto a surface of theepoxide-based matrix to form the chloride selective membrane, whereinthe membrane is provided with a plurality of quaternary functionalgroups; and wherein the chloride selective membrane is stable for atleast 14 days upon exposure to at least one biological sample.
 10. Theprocess of claim 9, wherein the amino compound comprises a tertiaryamine.
 11. The process of claim 10, wherein the tertiary amine comprisesa member selected from the group consisting ofN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA);N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA); andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA).
 12. The process of claim10, wherein the tertiary amine comprises a polyamine, and wherein anunsaturated and unsubstituted carbon chain is present between two aminogroups in the polyamine.
 13. The process of claim 9, wherein theactivator comprises a mercaptan compound.
 14. The process of claim 13,wherein the mercaptan compound comprises a member selected from thegroup consisting of pentaerythritol tetrakis (3-mercaptopropionate),Trimethylolpropane tris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate).
 15. The process of claim 9, wherein theepoxide-based matrix comprising an epoxy resin and comprises a liquidreaction product between epichlorohydrin and bisphenol A (DER 331). 16.A process of detecting chloride in at least one biological sample, theprocess comprising the steps of: contacting a chloride selectiveelectrode with at least one biological sample, wherein the chlorideselective electrode comprises a chloride selective membrane providedwith a plurality of quaternary functional groups, and wherein thechloride selective membrane comprises: an epoxide-based matrixcomprising an epoxy resin having a predetermined number of epoxidegroups per molecule; and a mixture of an amino compound and an activatordispensed onto a surface of the epoxide-based matrix, wherein the aminocompound and activator are present in the mixture in a stoichiometricamount relative to the number of epoxide groups in the epoxide-basedmatrix, and wherein the stoichiometric amount is in a range of fromabout 0.5:1 to about 1.5:1, and wherein the mixture comprises reactivespecies; and determining that chloride is present in the at least onebiological sample based on detection of a potentiometric signalgenerated upon reaction between the quaternary ammonium sites on thechloride selective membrane and chloride present in the at least onebiological sample.
 17. The process of claim 16, wherein the chlorideselective electrode is disposed in a sensor comprising a housing, asensor plate on which the chloride selective membrane is formed, and atleast one electrical connector configured to detect the potentiometricsignal.
 18. The process of claim 17, wherein the sensor is present in asensor assembly, and wherein the sensor assembly further comprises atleast one additional sensor for detecting an ionic species selected fromthe group consisting of sodium, potassium, magnesium, and calcium. 19.The process of claim 16, wherein the chloride selective membrane isstable for at least 14 days following exposure to the at least onebiological sample.
 20. The process of claim 16, wherein at least one of:the amino compound comprises a tertiary amine, wherein the tertiaryamine comprises a member selected from the group consisting ofN,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHA);N,N,N′,N′-Tetramethyl-2-butene-1,4-diamine (TMBEA); andN,N,N′,N′-Tetramethyl-1,4-butanediamine (TMBA); the amino compoundcomprises a tertiary amine, wherein the tertiary amine comprises apolyamine, and wherein an unsaturated and unsubstituted carbon chain ispresent between two amino groups in the polyamine; the activatorcomprises a mercaptan compound comprising a member selected from thegroup consisting of pentaerythritol tetrakis (3-mercaptopropionate),Trimethylolpropane tris(3-mercaptopropionate), and ethylene glycolbis(3-mercaptopropionate); and the epoxide-based matrix comprises aliquid reaction product between epichlorohydrin and bisphenol A (DER331).